Japanese has a large inventory of sound symbolic or mimetic words, known in linguistics as ideophones (Hamano 1998; Voeltz & Kilian-Hatz 2001). Sound symbolic words are found in written as well as spoken Japanese (Nuckolls 2004). Known popularly as onomatopoeia, these words are not just imitative of sounds but cover a much wider range of meanings (Hamano 1998); indeed, many sound-symbolic words in Japanese are for things that don't make any noise originally, most clearly demonstrated by しいんと shiinto, meaning "silently".

words that mimic actual sounds. Giseigo refers to sounds made by living things, while Giongo refers to sounds made by inanimate objects.

Phenomime (擬態語 gitaigo)

words that depict non-auditory senses.

Psychomime (also called 擬態語 gitaigo or 擬情語 gijōgo)

words that depict psychological states or bodily feelings.

In Japanese grammar, sound symbolic words function as adverbs. Just like ideophones in many other languages, they are often introduced by a quotative complementizer と (to) (Kita 1997:384). Most sound symbolic words can be applied to only a handful of verbs or adjectives. In the examples below, the classified verb or adjective is placed in square brackets.

In their Dictionary of Basic Japanese Grammar, Seiichi Makino and Michio Tsutsui point out several other types of sound symbolism in Japanese, that relate phonemes and psychological states. For example, the nasal sound [n] gives a more personal and speaker-oriented impression than the velars[k] and [ɡ]; this contrast can be easily noticed in pairs of synonyms such as ので node and から kara which both mean because, but with the first being perceived as more subjective. This relationship can be correlated with phenomimes containing nasal and velar sounds: While phenomimes containing nasals give the feeling of tactuality and warmth, those containing velars tend to represent hardness, sharpness, and suddenness.

Similarly, i-type adjectives that contain the fricative [ɕ] in the group shi tend to represent human emotive states, such as in the words 悲しい kanashii (sad), 寂しい sabishii (lonely), 嬉しい ureshii (happy), and 楽しい tanoshii (enjoyable). This too is correlated with those phenomimes and psychomimes containing the same fricative sound, for example しとしとと降る shitoshito to furu (to rain / snow quietly) and しゅんとする shun to suru (to be dispirited).

The use of the gemination can create a more emphatic or emotive version of a word, as in the following pairs of words: ぴたり / ぴったり pitari / pittari (tightly), やはり / やっぱり yahari / yappari (as expected), 放し / っ放し hanashi / ppanashi (leaving, having left [something] in a particular state), and many others.